Print stack trace when child fails to contact parent.

git-svn-id: https://svn.apache.org/repos/asf/lucene/hadoop/trunk@380834 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/hadoop/mapred/TaskTracker.java

@@ -656,7 +656,7 @@ public class TaskTracker implements MRConstants, TaskUmbilicalProtocol, MapOutpu
                   try {
                     umbilical.ping(taskid);
                   } catch (Throwable t) {
-                    LOG.warning("Parent died.  Exiting "+taskid);
+                    LOG.log(Level.WARNING, "Parent died.  Exiting "+taskid, t);
                     System.exit(1);
                   }
                   try {